Three dimensional (3D) time-of-flight (TOF) cameras are active optical depth measurement systems. In general, TOF systems are based on the phase-measurement technique of emitted intensity-modulated light, which is reflected by the scene. The reflected light is imaged onto a sensor. The photo-generated electrons are demodulated in the sensor. Based on the phase information, the distance for each pixel is deduced. A more detailed description is presented by Oggier, et al. in “An all-solid-state optical range camera for 3D real-time imaging with sub-centimeter depth resolution (SwissRanger)”, Proc. Of the SPIE, Vol. 5249, pp. 534-545, 2004.
All TOF cameras include an illumination module, an imaging sensor and some optics. The illumination module is designed such as to illuminate the scene so as to enable its capture as uniformly as possible, or adjust the illumination based on the scene of interest.
All existing full field TOF cameras illuminate the pixels of interest simultaneously with an illumination module that comprises either an array of light emitting diodes (LEDs) or laser diodes. The illumination module is designed with the intention to keep the required dynamic range of the sensor as small as possible, often leading to adjustments that result in the reflection of the same amount of light back to the camera from all objects within the field of interest. In general purpose 3D TOF cameras, the illumination is built to illuminate the field-of-view as uniformly as possible.
Optimal illumination beam shaping for TOF cameras are presented by Oggier et al. in “Time of Flight Camera with Rectangular Field of Illumination”, U.S. Pat. Appl. Publ. No. US 2011/0025843 A1. Further improvements can be achieved using masked illumination as suggested by Oggier et al. in “3D TOF camera with masked illumination”, U.S. patent application Ser. No. 13/196,291, filed on Aug. 2, 2011. Other approaches using diffractive optical elements or other refractive devices are possible to improve the illumination.